Thin film of CuInS2 deposited by thermal evaporation method. Initially the film was pinhole free. After few hours pinholes created in film and the no. Of pinholes keep on increasing even though it is kept in vacuum. Can anyone suggest the solution for this problem?
Dear Dr. Sivagami
Deposit the film at higher vacuum than what you are using at present. For good adhesion, Degass the substrates before deposition. Make slightly thicker films. Anneal them after evaporation in vacuum at higher temperatures for getting rid of voids. See if you are able to solve the problem. Substrate cleaning can also be improved for better uniformity. Good luck.
Thank you sir.can you kindly suggest me the ways to degass the glass substrates?
If substrates are glass plates, degassing is done by putting a heater inside the coating unit over the substrates and heat them up to 200 degree centigrade for about two hours in vacuum. The gasses absorbed comes out in this process. Switch off the heater to cool down to room temperature. Thereafter, deposit the film without exposing them to air.
pinholes are mainly created due to any foreign material already present in the substrate and they tries to come out through the deposited films during deposition. Clean your substrate thoroughly in piranha solution (1:1 ratio of H2O2 and H2SO4 for 20 min. ** you can search in net for details) . Thereafter rinse in DI water and preheat in oven @ 150 deg. Cent. for at least 30 min and then place in thermal chamber for deposition. Also you should heat your substrate up to 150 deg. cent. just before deposition. For better film quality high vacuum is essential.
Pinholes are either caused by surface contamination remaining on the "cleaned" surface. Use the water break test to determine if the surface is residue free. You will see interference fringes as it dries. The fringes will be even as the water evaporates. Any island fringes or streaks means the surface is not clean. Any of these particles actually become nucleation sites as the coating is deposited.
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